1. Field of the Invention
The invention relates generally to circuit boards and in particular to optical circuit boards.
2. Background Information
Meeting the requirements of highly integrated systems requires bringing communication interfaces such as communication optics closer to the microprocessors. This in turn requires interconnecting sub-assemblies and carrying electro-optic transceiver modules to chip carriers. However, temperature excursions (including the soldering operations for modules or chip on carriers) can damage optics. Optical parts are not designed for exposure to high temperatures or to multiple temperature cycles with temperatures involved in soldering cycles (e.g., 230° C. and above).
Conventional implementations utilize flexible circuits (e.g., made of Polyimide PI, Liquid Crystal Polymer LCP, Benzocyclobutene BCB, and other materials) that are soldered to a matrix of contacts (loosing field upgradeability/repair options), or mounted by the use of Z-axis interconnection materials (e.g., in the form of foils, rubber, matrix of contacts).
Interconnection materials such as electrical interposers are usually polymers/plastics loaded, using different techniques, with metal particles in the form of needles, flakes, spheres or other shapes. When these interposers are compressed by a vertical load, the dispersed metal particles come in contact between the interposers and provide a vertical electrical connection/path between the two opposite surfaces of the interposer material, establishing an electrical connection, for example, between the flex cable and the substrate. This vertical connection allows the transfer of electrical signals which are then transferred to the optical devices mounted on the flex substrate.
Interposers represent a further mounting step in the sequence of product assembly, and also represent at least a further double interface (i.e., flex to interposer and interposer to chip carrier), negatively affecting quality of the electrical signal being transmitted (signal degradation due to impedance/transmission line discontinuities on the transmission line and Ohmic resistance in the electrical interconnect).